The present invention relates to a new and distinct cultivar of blueberry, which is cold-hardy and low-statured and presents a combination of unique characteristics. This new variety originated from a hand pollinated, interspecific hybridization of Minnesota Selection B-6.times.Minnesota Selection 69-3, which was made by inventor Cecil Stushnoff in 1969 at the Horticultural Research Center of the University of Minnesota, located near Excelsior, Minn.
The seeds resulting from such hybridization were germinated in 1969 and the resulting seedlings were planted in the spring of 1971 in a field research plot of the University of Minnesota located near Elk River, Minn. In 1975, several thousand of such seedlings were moved from the Elk River, Minn. site to other experimental sites in Minnesota, for further testing. The seedling which was subsequently selected as the present variety was one of a large number of such seedlings assigned to co-operator and co-inventor Cy Milbrath, for further testing at his nursery located in northern Minnesota. Such nursery is known as Marcy Blueberry Nursery and is located on the shore of Crystal Lake, approximately 16 miles south of Virginia, Minn. Specifically, such nursery is 1/3 mile west of U.S. Highway 53 on County Road 621, in St. Louis County. Following several years of over-wintering and summer fruiting, the superior performance characteristics of the present variety compared to other named cultivars and numerous other seedlings derived from the above-noted hybridization, including lack of winter injury, were recognized by the co-inventors named herein, and in 1978 the seedling of this variety was identified as M-30.
The original selection of the present variety, designated M-30, has been propagated asexually by the rooting of softwood cuttings, and a test planting of seventeen plants was established at the above-noted nursery of Cy Milbrath. The original plant of the present variety has been observed each year for the past 18 years, and since 1975 data has been collected on winter injury relative to meteorological climatic conditions.
This new variety has demonstrated superior performance with respect to two important characteristics of cold hardiness, which are mid-winter survival and spring flower bud hardiness. Mid-winter survival of this new variety is evident from both exposure to severe freezing events during the past 18 years at the above-noted northern Minnesota location adjacent Crystal Lake, Minn., as well as from controlled freezing tests made under laboratory conditions.
The above-noted Crystal Lake, Minn. test site at the nursery of co-inventor Cy Milbrath is located in USDA winter hardiness map zone 3a, where minimum temperatures attain -35.degree. F. as determined by 35 year temperature records. A low temperature of -45.degree. F. was recorded Dec. 31, 1976, at Virgina, Minn., which is approximately 16 miles north of the test site at Crystal Lake, Minn. It is therefore likely that the original test plant has been exposed to at least -40.degree. F. and has survived 18 years at the test site located near Crystal Lake, Eveleth, Minn. Controlled freezing tests have shown survival of stems frozen at -8.degree. F. per hour, down to -40.degree. F., and survival of flower buds down to -25.degree. F.
Blueberry plants are typically of the low-bush or high-bush variety. The low-bush types have good fruit flavor and usually have fruit set because the low plant stature normally is covered by snow. The high-bush types normally have higher fruit production but the berry flavor may not be as desirable and the plants are generally not as winter hardy. This new variety has the fruit flavor characteristic of the low bush types, but with the increased fruit production of the high-bush types, and the variety also has considerable winter hardiness.
One of the problems with respect to the blueberry hardiness is survival of flower buds during below-freezing periods in the spring. On Apr. 29, 1990, the flower buds on plants of this variety survived a temperature of 22.degree. F., as well as a temperature of 23.degree. F. on Apr. 30, 1990, at the above-noted nursery test site at Crystal Lake, Eveleth, Minn., and later that summer produced a crop of fruit. With such frost conditions on Apr. 29-30, 1990, all other selections and cultivars of blueberry plants located at the nursery test site at Crystal Lake, Eveleth, Minn. experienced flower bud damage, and none thereof produced any fruit that year.
The plants of this new variety are erect and moderately vigorous for low-statured blueberry plants. Plants of this variety attain a height of 80 cm after three years and 95 cm at maturity. Two to three new shoots emerge from the base of the plants each year, but the narrowness and openness of the plant indicates that the present variety may likely be suitable for mechanical harvesting of fruit. The new growth of stems is light green in color, changing to crimson in the autumn. New growth may be distinguished by its pubescent (fuzzy) texture of the stems. The pubescence remains on the stems and appears to be a distinguishing feature as compared to other varieties of blueberries observed by the inventors. The leaves are dark green to blue-green in color and 20-25 mm wide and 40-50 mm in length.
Lateral flower buds form on first year shoot growth. The flowers are white with 6-8 flowers per cluster. Flowering occurs from the 3rd week in May through the 2nd week in June at the above-noted test site near Crystal Lake, Eveleth, Minn. It has also been observed that the new flower buds which form in the autumn tend to curl or close up in late fall.
With respect to berry production, the berries begin maturation for harvest about the third week in July and may be harvested until mid-August, at the above-noted nursery test site at Crystal Lake, Eveleth, Minn. The berries of this new variety are similiar in size to large low-bush blueberries, range from 5 mm to 13 mm in diameter, and average 6 mm.times.9 mm in size. A light bloom covers the medium blue colored berries, which have a small dry scar. The berries are medium to firm and resemble the fruit on low-bush blueberry plants, and during normal seasons it is believed that this new variety may be suitable for mechanical harvesting of fruit.
The berries on this new variety are highly flavored, similar to low-bush blueberries, and posssess a good balance of sugar to acid, have normal skin thickness and small seeds. Fruit of this variety which has been frozen, has stored very well.
This new variety has exhibited no evidence of infestation of common blueberry diseases, such as stem blight, cane canker and witches broom, but precise levels of resistance to diseases will require more observation and testing.
The combination of characteristics of this new variety which are believed to be unique include winter hardiness, spring flower bud hardiness, medium berry size, low leaf density, the open structure of the lower plant branches which permits access to berries and possible mechanical harvesting of fruit, generally heavy fruit set, the manner in which the flower buds close up in autumn and the flavor and quality of the berries.